The present invention relates to packs used in outdoor backpacking, and more particularly to a new and improved support device for an internal frame backpack.
In the field of outdoor sport backpacking, there are several distinct styles of packs. Common day packs are used by students to carry books, or by hikers to carry provisions for a very short trips (picnics or hikes) lasting usually less than a full day. Such day packs usually include two zipper-closed compartments (a large one and a pocket-sized one), and a pair of adjustable shoulder straps. Larger frameless overnight packs are available to provide more space for supplies for a single night outdoors. Finally, extended trip frame packs are available for trips lasting several days or weeks.
For extended trip backpacking enthusiasts, there are at least two distinct styles of packs that are widely used: external frame packs and internal frame packs. External frame packs are generally characterized by one or more large compartments (the pack) having several various sized pocket compartments sewn thereto all of which is attached to a metal frame. The frame is outside of and external to the compartments of the pack, and is attached to the pack by stitches, bolts or other similar means. Two shoulder straps and a waist belt are typically attached to the frame, and not to the pack itself, so that the frame acts as the support for the pack. In use, parts of the metal frame are visibly apparent between the wearer and the pack.
Internal frame packs are generally characterized by one or more large compartments (the pack) having several various sized pocket compartments sewn thereto, on the inside of which a metal support frame (usually in the form of two metal strips or stays mounted in a parallel pattern) is placed. Typically, one or more tubular sleeves are sewn onto the inside of the largest, lower compartment of the pack (in a parallel pattern) into which the metal strips are slidably placed. In place, these strips define a rigid surface on the otherwise flimsy pack. On the outside of this rigid surface the shoulder straps and waist belt are attached, so that the weight of the load in the pack is transferred to the waist belt of the user, and not the shoulders.
Internal frame packs are typically used in winter camping where the user is on skis and requires a low center of gravity. Other uses for internal frame packs are for rock climbing or other technical camping where the bulk of an external frame might inhibit or endanger the wearer. The most important benefit of an internal frame pack is that it fits closely to the body of the user. This close fit provides warmth as well as a low center of gravity, and the separate strips of the internal frame allow the pack to move with the user (torsional flex) during skiing or technical climbing.
External frame packs are generally used in non-technical summer backpacking and hiking. The rigidity of the external frame provides a much more efficient transfer of the load in the pack to the waist belt of the user than an internal pack. However, the same rigidity of the external frame prohibits such a pack from moving or bending with the user during climbing, etc.
One of the most common problems presented by internal frame packs is a lack of good support by the internal frame itself. A very full pack will protrude slightly below and significantly above the frame itself, often to the point where the frame provides little more than a location at which the user wears the pack. Weight shifting above the frame tends to put the whole pack off balance, and the frame does little by way of compensating for it. The greater the load, the more deformed the support strips become. Thus, with larger loads, weight transfer to the waist belt is often very inefficient.
Other related problems with internal frame packs are the discomfort and fatigue suffered by the wearer because the frame is, by definition, flimsy and insubstantial. As more is loaded into the pack, it bows away from the user's back (in a barrel shape) failing to transfer the load to the waist, and instead putting more of the load on the user's shoulders.